Field of the Invention
The present invention relates to movable body drive methods and movable body drive systems, pattern formation methods and apparatuses, exposure methods and apparatuses, and device manufacturing methods, and more particularly to a movable body drive method in which a movable body is driven within a movement plane and a movable body drive system, a pattern formation method using the movable body drive method and a pattern formation apparatus equipped with the movable body drive system, an exposure method using the movable body drive method and an exposure apparatus equipped with the movable body drive system, and a device manufacturing method in which the pattern formation method is used.
Description of the Background Art
Conventionally, in a lithography process for manufacturing microdevices (electron devices and the like) such as semiconductor devices and liquid crystal display devices, exposure apparatuses such as a projection exposure apparatus by a step-and-repeat method (a so-called stepper) and a projection exposure apparatus by a step-and-scan method (a so-called scanning stepper (which is also called a scanner) are relatively frequently used.
In this kind of exposure apparatus, in order to transfer a pattern of a reticle (or a mask) on a plurality of shot areas on a wafer, a wafer stage holding the wafer is driven in an XY two-dimensional direction, for example, by linear motors and the like. Especially in the case of a scanning stepper, not only the wafer stage but also a reticle stage is driven in by predetermined strokes in a scanning direction by linear motors and the like. Position measurement of the reticle stage and the wafer stage is generally performed using a laser interferometer whose stability of measurement values is good for over a long time and has a high resolution.
However, requirements for a stage position control with higher precision are increasing due to finer patterns that accompany higher integration of semiconductor devices, and now, short-term variation of measurement values due to temperature fluctuation of the atmosphere on the beam optical path of the laser interferometer has come to occupy a large percentage in the overlay budget.
Meanwhile, as a measurement unit besides the laser interferometer used for position measurement of the stage, an encoder can be used, however, because the encoder uses a scale, which lacks in mechanical long-term stability (drift of grating pitch, fixed position drift, thermal expansion and the like), it makes the encoder have a drawback of lacking measurement value linearity and being inferior in long-term stability when compared with the laser interferometer.
In view of the drawbacks of the laser interferometer and the encoder described above, various proposals are being made (refer to Kokai (Japanese Patent Unexamined Application Publication) No. 2002-151405, Kokai (Japanese Patent Unexamined Application Publication) No. 2004-101362 and the like) of a unit that measures the position of a stage using both a laser interferometer and an encoder (a position detection sensor which uses a diffraction grating) together.
Further, the measurement resolution of the conventional encoder was inferior when compared with an interferometer, however, recently, an encoder which has a nearly equal or a better measurement resolution than a laser interferometer has appeared (for example, refer to Kokai (Japanese Patent Unexamined Application Publication) No. 2005-308592), and the technology to put the laser interferometer and the encoder described above together is beginning to gather attention.
However, in the case position measurement is performed of the movement plane of the wafer stage of the exposure apparatus that moves two-dimensionally holding a wafer using an encoder, for example, in order to avoid an unnecessary increase in the size of the wafer stage and the like, it becomes essential to switch the encoder used for control while the wafer stage is moving using a plurality of encoders, or in other words, to perform a linkage between the plurality of encoders. However, as it can be easily imagined, for example, when considering the case when a grating is placed on the wafer stage, it is not so easy to perform linkage between a plurality of encoders while the wafer stage is being moved, especially while precisely the wafer stage is being moved two-dimensionally along a predetermined path.
Further, by repeating the linkage operation, the position error of the wafer stage may grow large with the elapse of time due to the accumulation of the error which occurs when linkage is performed, and the exposure accuracy (overlay accuracy) may consequently deteriorate.
Meanwhile, it is conceivable that the position of the wafer stage does not necessarily have to be measured using an encoder system in the whole movable range of the wafer stage.
Now, the propagation speed in the cable of an electrical signal such as the detection signal of the head of the encoder, or more specifically, the photoelectric conversion signal of the light receiving element is limited, and the length of the cable through which the detection signal of the encoder propagates is generally from several meters to 10 m, and in quite a few cases exceeds 10 m. When considering that a signal propagates through the cable of such a length at the speed of light, the influence of the delay time that accompanies the propagation is at a level that cannot be ignored.